The invention relates to an antenna diversity radio receiving arrangement for telecommunications systems using block-oriented transmission of radio messages.
Telecommunications systems using block-oriented transmission of radio messages are being technically developed, linked to various standards, analogous to the ISDN Standard (Integrated Services Digital Network) which has already been in existence for a relatively long time in cable-based telecommunications technology. The term "block-oriented transmission" essentially defines methods of transmitting radio messages which are transmitted using the time division multiple access method (TDMA=Time Division Multiple Access) or using the code division multiple access method (CDMA=Code Division Multiple Access). Known telecommunications systems, based on the TDMA method, are, for example, cordless telecommunications systems to the DECT Standard (Digital European Cordless Telecommunication) and mobile radio telecommunications systems to the GSM Standard (Global Systems for Mobile Communication).
A dynamic channel selection from about 120 available channels is carried out for cordless telecomunication to the DECT Standard (cf. European Telecommunication Standard -Final Draft-; prETS 300 175-1, 5/1992; ETS-Institute 06921 Sophia Antipolis, France). The 120 channels result from the fact that ten frequency bands between 1.8 and 1.9 GHz are used in the DECT Standard, a time division multiple access frame of 10 ms being used in the time division multiple access mode (TDMA=Time Division Multiple Access) in each frequency band, as illustrated in FIG. 1. 24 (from 0 to 23) time channels are defined in this time division multiple access frame and thus govern a frame layout. This frame layout is then used in such a manner that a maximum of 12 mobile sections PT (Portable Termination), which are assigned to a base station FT (Fixed Termination), of a DECT telecommunications system can operate simultaneously in the duplex mode (PT.fwdarw.FT and FT.fwdarw.PT as well as FT.fwdarw.PT and PT.fwdarw.FT) for each frequency band.
In this case, the 24 time channels are in each case assigned time slots having a time slot duration of 417 .mu.s. The time slot in this case indicates the time in which information (data) is transmitted. This transmission of information in the duplex mode is also called the ping pong method since transmission is carried out at a specific time and reception is carried out at a different time. In this ping pong method, a burst having a time duration of 365 .mu.s or a bit length of 420 bits with a data throughput of 42 kBit/s is transmitted in each time slot. Taking account of the fact that 30 bits are in each case available in a security time frame GS (Guard Space) at both ends of the time frame in order to avoid adjacent time slots overlapping, this results in a total data throughput of 1.152 MBit/s with respect to the time division multiple access frame. The chronological sequence of the transmitted pulses per time division multiple access frame defines, according to FIG. 2, a PH channel, the so-called physical channel, which is assigned to a so-called physical layer (PH-L). The data package of 420 bits transmitted in this case is called a PH package and is assigned to a D field. Of the 420 data bits (sequence of H/L bit values) in the PH packet, 32 bits are used for synchronization to a synchronization field SYF, and 388 bits are used for the transmission of wanted information to a wanted information field NIF.
The 32 bits in the synchronization field SYF are in turn divided into two data bit sequences of 16 bits each. The first data bit sequence (sequence with the first 16 H/L bit values) is a synchronization initiation word SEW, which is used to initiate synchronization. For a transmission direction "mobile section PT.fwdarw.base station FT", this synchronization initiation word SEW ideally comprises a periodic "101" or "TLH" sequence, and a likewise periodic "010" or "LEHL" sequence for the opposite transmission direction "base station FT.fwdarw.mobile section PT". The base station/mobile section assignments shown in brackets in FIGS. 1 and 2 are possible as alternatives depending on which sequence is assigned to which transmission direction.
The second data bit sequence (sequence with the second 16 H/L bit values) is a synchronization confirmation word SBW which must be used to confirm the synchronization initiated using the synchronization initiation word SEW. Essentially, the data bits of the synchronization confirmation word SBW must be identified with this confirmation. Only if this is the case is the synchronization initiated using the synchronization initiation word SEW accepted. The synchronization is in this case initiated if it is possible to assume, with a certain probability, that the synchronization initiation word SEW is an "HLH" or "LHL" sequence.
Furthermore, other layers are also defined in the DECT Standard, analogous to the ISDN Standard using the ISO/OSI 7-layer model. One of these layers is a medium access control layer (MAC-L) to which, according to FIG. 3, the 388 bits in the wanted information field NIF are assigned for transmission of wanted information. The wanted information field NIF is in this case composed of an A field and a B field. The A field comprises 64 bits of the 388 bits in the wanted information field NIF and these are used, inter alia, for messages when the base station is connected to the mobile sections of the DECT telecommunications system. The other 324 bits are assigned to the B field, 320 bits thereof being used for voice data and 4 bits to identify partial interference of the pulse. Finally, the 324 bits in the B field are assigned to other ISO/OSI layers in the context of the ISO/OSI 7-layer model.
In the simplest form, the DECT telecommunications system has a base station with at least one mobile section. More complex (for example network) systems contain a plurality of base stations, each having a plurality of mobile sections. On the basis of the 24 time channels defined in the DECT Standard, up to 12 mobile sections can be assigned to the base station, which communicate with the base station using the duplex mode. For the time division multiple access frame, which is likewise defined in the DECT Standard, of 10 ms, the duplex mode means that information is transmitted from the base station to the mobile section, or vice versa, every 5 ms.
When transmitting radio-frequency-modulated radio messages--for example DECT radio messages in the GHz band--, the transmission conditions frequently differ very considerably within a small physical region of a few centimeters (centimetric region) because of the propagation characteristics of the radio-frequency carrier signal. In the case of mobile systems, such as the DECT telecommunications system, this results in the transmission conditions fluctuating greatly with time even at low speeds of about 1 m/s. In order to counter at least partially these time fluctuations in the transmission conditions, it is known for a second, physically offset antenna to be installed at least at one part of the mobile system (for example the base station). Because of the physical separation, the reception conditions at the antennas differ and can be selected by antenna switching. This method, which is known by the term "antenna diversity" (cf. Proceedings of International Conference on Communications--ICC'91; Jun. 23-26, 1991, New York (US), pages 1480 to 1484 and Patent Abstracts of Japan, Vol. 11, No. 231 (E-527), Jul. 28, 1987 in conjunction with JP-A-62047222) enables improved reception of radio messages in mobile systems when the transmission conditions are poor in places. The antenna diversity method is suitable in particular for DECT telecommunications systems based on the TDMA method, in the case of which it is possible to change the antenna in the time between two time slots without this interfering with the transmitted radio message.
If, according to FIGS. 4 and 5, at least two antennas A1, A2 but only one receiver REC, which is assigned to a radio section RE, RE-T, RE-R of the antenna diversity radio receiving arrangement FT, PT, are used in an antenna diversity radio receiving arrangement FT, PT which is known from WO 94/10812 (for example a base station and/or mobile section of a cordless telephone), then, according to WO 94/10764, there is a critical problem in the control of the antenna diversity switching in that the reception conditions cannot be assessed simultaneously at the two antennas. It is therefore proposed that the reception conditions be checked once per time slot, for example by a field strength measurement and/or evaluation of transmission errors (CRC errors: Cycle Redundancy Check). These current and preceding checks, which are related to time slots, are used to decide whether the radio message transmitted In the subsequent time slot will be received on the same antenna or on a different antenna. However, since the transmission conditions can change severely in the time between two time slots, this known antenna diversity method does not guarantee that the chosen antenna offers the best possible reception at this time.
Furthermore, U.S. Pat. No. 5,241,701 discloses an antenna diversity radio receiving arrangement for telecommunications systems using block-oriented transmission of radio messages, in which the antenna diversity means assigned to the radio receiving arrangement and having two antennas assigned thereto are designed in such a manner that, during the receiving of time duration a message block (time slot) of the radio message, at least two different antennas, which are assigned to the antenna diversity means, are assigned alternately to the receiving channel of the antenna diversity radio receiving arrangement, as the receiving antenna.